It was shown earlier that a cross-reactive idiotype (CRI) associated with antiphenylarsonate (anti-Ar) antibodies of A/J mice can be suppressed by injection of antiidiotypic serum. Suppressed mice produce anti-Ar antibodies with "private" idiotypes that are generally undetectable in the anti-Ar antibodies of other A/J mice. Amino acid sequences of homogeneous subpopulations of these private idiotypes would be of interest. Recent studies suggest the feasibility of the project. A private idiotype can be transferred adoptively into an irradiated (200 R) recipient by spleen cells from a hyperimmune suppressed (HIS) mouse, followed by immunization. Serial transfers can be carried out; this sometimes results in "dilution" of the idiotype. A more effective method is to induce an HIS mouse to produce ascites, which contains leukocytes. A single donor has been used to suppress as many as 12 recipients which produced a high concentration of the private idiotype. Ascitic fluids containing antibodies can then be induced in the recipients; thus, large amounts of the private idiotype can be produced without serial transfer. Isoelectric focusing should establish whether homogeneous subpopulations are present; also, using labeled subfractions as ligands, data should emerge as to the degree of diversity of anti-Ar antibodies in strain A mice. Other studies are designed to determine the nature of the Ly antigens on the suppressor T cells. A potential mechanism of suppression may involve "clonal dominance" of the large number of B cells in a HIS mouse after adoptive transfer. Studies are outlined to determine whether this is a significant factor. Direct studies of competition among B cells will also be carried out with mixtures of cells from different HIS donors of defined idiotype. We will also use idiotypically suppressed recipients to test the hypothesis that suppressor T cells are generated by the interaction of anti-id antibodies and small amounts of the idiotype in a suppressed animal. Attempts will be made to isolate the active factor from suppressor T cells. Other studies are based on the observation that HIS mice contain splenic cells (mainly T cells) which form rosettes with autologous red blood cells coated with the CRI. We plan to determine whether the rosette-forming cells include the suppressors. (Current assays by adoptive trans (Text Truncated - Exceeds Capacity)